This invention relates to retainers that keep an engine valve seat in a substantially fixed position. More particularly, this invention relates to such retainers manufactured using a rolling apparatus and method.
Valve seats are used in internal combustion engines to seat the intake and exhaust valves. The valve seats are typically distinct components from the engine block, but are interconnected with the block during the engine manufacturing process.
It is essential that the valve seat remains in a substantially fixed position during engine operation. If the valve seat is loosened or displaced altogether, the engine will not operate properly and may fail.
Several methods are known to retain a valve seat in a substantially fixed position. In one prior art method, the valve seat is simply press-fit into a recess in the engine block. A disadvantage of this approach is that the aluminum composite material from which the engine block is made expands at a higher rate than the valve seat. At engine operating temperatures, the valve seat may loosen or dislodge altogether when the engine block material expands in a direction away from the valve seat.
Rolling methods have also been used to create retainers for valve seats. U.S. Pat. No. 2,008,002 issued Jul. 16, 1935 to Calkins and U.S. Pat. No. 1,795,433 issued Mar. 10, 1931 to Leipert both disclose the manufacture of valve seat retainers using a rolling method. U.S. Pat. No. 1,949,614 issued Mar. 6, 1934 to McDonald discloses a preening method. In each of these prior art methods, a small amount of material from the engine block is moved over the valve seat to create an overhang or flange that is intended to retain the valve seat in place. The flange typically extends about 0.003 to 0.005 inches over the valve seat.
Unfortunately, these prior art rolling and preening methods have disadvantages which are similar to the press-fit method discussed above. In these prior art rolling and preening methods, the cylinder block material has a higher thermal rate of expansion than the valve seat, so that the valve seat may loosen at engine operating temperature. The loosened valve seat moves back and forth in its recess, repeatedly striking the overhanging flange. Since the flange is relatively short in length when made according to these prior art methods, the flange may break off, allowing the valve seat to become totally dislodged.